1. Field of Invention
This invention pertains to metalization of electronic semiconductor devices.
2. Description of Prior Art
the AuGe/Ni/Au and AuGe/Au metalization schemes are commonly used in GaAs-based and InP-based devices. Also, the most commonly reported source-drain contacts for AlSb/InAs-based semiconducting materials have been AuGe/Ni/Au or AuGe/Au. However, in such contact schemes for the AlSb/InAs meterials, the contact resistance values are commonly high and the contacts are difficult to adhere. With such schemes, there is significant lateral diffusion into the channel as a result of rapid thermal annealing, which imposes a limit on the minimum HEMT source-drain spacing. Furthermore, scanning electron microscopy revealed that a region of the semiconducting material reacted, as a result of the heat treatment, and extended laterally inwardly from each contact edge.
Semiconducting devices fabricated using the AlSb/InAs-based material systems have potential applications in the fields of high-speed logic and millimeter-wave circuits. AlSb/InAs-based systems have potential for high-speed applications due to the large conduction band discontinuity and attractive transport properties of the InAs channel. Although improvements have been made in recent years, the material growth and fabrication technology for AlSb/InAs devices is relatively immature. The reduction of the source and drain access resistance in semiconducting electronic devices, such as HEMTs, is an area where improvement is needed. Low access resistance is required to reduce the parasitic delays which can significantly mask the intrinsic speed in high-speed electronic devices, such as HFETs. The AlSb/InAs material system is particularly suitable for achieving low access resistance due to the high mobility, high sheet charge density, and low contact resistance values which are obtained.
Pd/Ge-based metalization have been used for ohmic contacts to GaAs-based and InP-based materials. These contacts are shallow, thermally stable, and able to provide low contact resistance via solid state reaction using a relatively low heat treatment.
In AlSb/InAs materials, Pd/Ge/Au contact schemes resulted in significant lateral diffusion into the channels when the sample was heat treated on a hot plate at a relatively low temperature. This deleterious lateral diffusion is a considerable drawback which limits usefulness of the Pd/Ge-type contact for AlSb/InAs-based heterostructures.
An object of this invention is a metallized semiconductor device containing metallic contacts of low contact resistance compared to prior art.
Another object of this invention is a process for forming a metallized semiconductor electronic device using a low temperature heat treatment which avoids material deterioration.
These and other objects of this invention are accomplished by a metallized semiconductor electronic device, such as an AlSb/InAs-based HFET, which has ohmic contact Pd/barrier/Au bonded to the device with contact resistance of less than 0.2 ohm-mm, access resistance of less than 0.5 ohm-mm, and a spacing between source and drain of less than 1 micron.